1. Field of the Invention
This invention relates to an electronic circuit board case, particularly to a case for housing an electronic circuit board, more particularly to a case for housing an electronic circuit board composed of a case body formed with an opening at at least one end and a sealing member for sealing the opening.
2. Description of the Related Art
In a case for housing an electronic circuit board composed of a case body formed with an opening at at least one end and a sealing member for sealing the opening, the sealing member is commonly attached to the case body using a hook-like fastening member (catch 100) such as shown in FIG. 18. The catch 100 comprises an elastically deformable leg 102 and a projection 104 continuous therewith. It is formed on one or the other of the case body and the sealing member.
The sealing member is attached to the case body by engaging the projection 104 of the catch 100 with a prescribed region 106 of the case body or the sealing member, as the case may be.
The catch 100 of the prior art is, however, disadvantageous in the point that should the vertical distance h from the contact surface 108 between the case body and the sealing member to the prescribed region 106 be formed small (as indicated by the doted lines in the drawing) owing to molding error, play will arise in the lateral and vertical directions.
In order to prevent this drawback, the height h of the catch 100 must be strictly controlled. Such strict dimensional control is disadvantageous from the cost aspect. In addition, the case body and sealing member (including the catch 100) experience repeated thermal expansion and thermal contraction when used in an environment subject to extreme temperature changes. If the case for housing an electronic circuit board is designed based on the dimensions during thermal expansion, lateral and vertical play is liable to arise during thermal contraction.
On the other hand, if the design is based on the dimensions during thermal contraction, excessive stress comes to act on, and may break, the catch 100 during thermal expansion. The catch 100 also becomes susceptible to damage under the action of large stress produced by vibration or the like.
The electronic circuit board can also be fastened at a prescribed location in the case by clamping it between the case body and the sealing member (cover or the like), as taught by Japanese Laid-Open Patent Application No. 9(1997)-230069, No. 7(1995)-302984, No. 7(1995)-249881 and No. 5(1993)-283876, and Japanese Utility Model Registration No. 2586966. This expedient encounters the same disadvantage, however, owing to molding error in the electronic circuit board thickness and/or volumetric variation caused by temperature changes.
Moreover, an adhesive is sometimes applied at the contact surface 108 between the case body and the sealing member in order to improve watertightness and fastening strength. When this is done, the same disadvantage is also likely to occur owing to irregular adhesive coating thickness and change in the height h produced by thermal expansion of the adhesive coating.
A first object of the present invention is therefore is to overcome the aforesaid problem by providing a case for housing an electronic circuit board that can tolerate greater molding error than the prior art and that can readily cope with stress produced by temperature change and vibration.
After the case body and the sealing member have been fastened together, there is a possibility of the sealing member separating from the case body should someone such as a worker touch the leg 102 with a force strong enough to elastically deform the leg 102 and release the engagement between the prescribed region 106 and the projection 104.
A second object of the present invention is therefore to provide a case for housing an electronic circuit board that prevents a worker or the like from contacting the leg and thus prevents separation of the sealing member from the case body.
The case for housing an electronic circuit board should preferably enable removal of the sealing member from the case body at the time of servicing and inspection.
A third object of the present invention is therefore to provide a case for housing an electronic circuit board that prevents separation of the sealing member from the case body but makes their separation possible as desired when necessary.
In order to achieve the foregoing objects, this invention in a first aspect provides a case for housing an electronic circuit board comprising: a case body formed with an opening at at least one end and a sealing member for sealing the opening, wherein one of the case body and the sealing member is formed with at least one fastening member composed of an elastically deformable leg and a projection continuous therewith for enabling attachment of the sealing member to the case body by engagement of the fastening member with a prescribed region of the other of the case body and the sealing member, the projection being continuous with at least the leg and having a first surface formed to contact the prescribed region at a prescribe angle and a second surface continuous with the first surface and formed parallel or substantially parallel to the prescribed region.
The projection of the fastening member (catch) is constituted to have the first surface that is continuous with at least the elastically deformable leg and is formed to contact the prescribed region to be engaged at a prescribed angle. Specifically, the prescribed region and the first surface form the prescribed angle and contact each other tangentially. Since the tangent of the first surface and the prescribed region is variable within the range of the first surface, molding error can be tolerated (absorbed) and stress owing to volumetric variation produced by temperature change or to vibration can be readily coped with. Moreover, due to the provision of the second surface formed continuous with the first surface to lie parallel or substantially parallel to the prescribed region, it is possible to prevent the tangent from leaving the range of the first surface, i.e., prevent release of the engagement of the projection with the prescribed region, and thus to prevent separation of the sealing member from the case body.
In a second aspect, this invention provides a case for housing an electronic circuit board, wherein the second surface is formed so as to lie parallel or substantially parallel to the prescribed region when the first surface contacts the prescribed region at or near the boundary with the second surface.
Since the second surface is formed so as to lie parallel or substantially parallel to the prescribed region when the first surface contacts the prescribed region at or near the boundary with the second surface, the tangent between the first surface and the prescribed region is reliably prevented from leaving the range of the first surface.
In a third aspect, this invention provides a case for housing an electronic circuit board, wherein one of the case body and the sealing member is provided with a cover for covering all or part of the leg when the projection is engaged with the prescribed region.
Since one of the case body and the sealing member is provided with a cover for covering all or part of the leg when the projection is engaged with the prescribed region, i.e., when the sealing member is attached to the case body, contact with the leg by a worker or the like is prevented, thereby preventing separation of the sealing member from the case body.
In a fourth aspect, this invention provides a case for housing an electronic circuit board, wherein one of the case body and the sealing member is formed with the leg at a location toward the case interior from a side wall.
Since one of the case body and the sealing member is formed with the leg at a location toward the case interior from a side wall, an effect similar to that of the third aspect is obtained, whereby contact with the leg by a worker or the like is prevented, thereby preventing separation of the sealing member from the case body.
In a fifth aspect, a case for housing an electronic circuit board is provided, wherein, in one of the case body and the sealing member, the prescribed region is a region within a space defined by the external shape of the case or sealing member and continuous with the external space.
Since in one of the case and the sealing member, the prescribed region is a region (location) within a space defined by the external shape of the case or sealing member and continuous with the external space, the sealing member can be prevented from separating from the case body while enabling its detachment whenever required.
In a sixth aspect, this invention provides a case for housing an electronic circuit board, wherein at least one first rib for mounting the electronic circuit board is formed in the case body and at least one second rib is formed in the sealing member, the first rib and the second rib clamping the electronic circuit board when the sealing member is attached to the case body.
Since at least one first rib for mounting the electronic circuit board is formed in the case body and at least one second rib is formed in the sealing member and the first and second ribs clamp the electronic circuit board when the sealing member is attached to the case body, the electronic circuit board can be reliably fastened at the prescribed location in the case.
In a seventh aspect, this invention provides a case for housing an electronic circuit board, wherein a recession or ridge is formed at the periphery of the opening of the case body and a ridge or recession for meshing with said recession or ridge so as to leave a prescribed intervening gap at which adhesive can be applied is formed in the sealing member.
Since a recession or ridge is formed at the periphery of the opening of the case body and a ridge or recession for meshing with said recession or ridge so as to leave a prescribed intervening gap at which adhesive can be applied is formed in the sealing member, watertightness and fastening strength can be enhanced.